UPD17P136ACT datasheet(136/292 Pages) NEC

136 / 292 page

CHAPTER 13 PERIPHERAL HARDWARE

117

13.1.5 Reading Value of Count Register

The values of the count registers of timers 0 and 1 are read simultaneously by using the GET instruction via DBF

(data buffer).

The values of the count registers of timers 0 and 1 are assigned to peripheral address 45H. The high-order 8 bits

of this address are assigned to the count value of timer 1, and the low-order 8 bits are assigned to the count value

of timer 0.

The values of the count registers can be read to DBF by using the GET instruction. While the GET instruction is

being executed, the count registers stop counting and hold the current count value. If a count pulse is input to the

timer while the timer is operating and the GET instruction is being executed, the count value is held, the value of the

count register is incremented by one after the GET instruction has been executed, and the timer continues counting.

Therefore, the timer does not count erroneously even if the GET instruction is executed while the timer is operating,

unless two or more count pulses are input to the timer in one instruction cycle.

Figure 13-5. Reading Count Value of Count Register

Example of using GET DBF, TM0TM1C; reserved word DBF and TM0TM1C

when count value of timer 0 is F0H and count value of timer 1 is A4H

Data buffer

DBF3

DBF2

DBF1

DBF0

101

010

0111

000

16-bit data

GET DBF, TM0TM1C

b15 b14 b13 b12

b11 b10

101

010

0111

000

TM0TM1C (peripheral address)

Timer 0 count value

Timer 1 count value

UPD17P136ACT Datasheet(PDF) 136 Page - NEC